Investigation of the effects of vertical link beam length on steel structures residual displacement

There is a debate among earthquake engineers that the structural and non-structural damages initially occur due to lateral loads caused by earthquake excitation. American provisions, including FEMA356 estimates structural performance by means of maximum deformation demand. However, in addition to the maximum deformation, residual displacement plays an important role in structural performance. Amplitude of residual displacement is an important parameter in technically and economically determining rehabilitation of damaged structures for resisting aftershocks. In this study, residual displacements of a five-story steel frame is designed with vertical link beam as well as the effect of vertical link beam length have been investigated. For vertical link beam, the IPE sections with typical steel is considered, instead of using boxes and H-shaped cross-section.The IPE section has some advantages than box section such as lower cost, easier installation and replacement. The Vertical link beams with IPE cross-section has been studied in 5 separate models with length of 20, 25, 30, 35 and 40 centimeters. In this paper, experimental results of a frame model with vertical link beam tested in structural laboratory of Building and Housing Research Center (BHRC) has been used for verification of numerical model. As one of the fastest nonlinear softwares, OpenSees (Open System for earthquake engineering simulation) has been used for structural modeling. The steel material that has been used in this model is uniaxial material steel 02. In the following, seven near field and seven far field earthquake acceleration time histories that scaled by 2800 standard, are used analysis of five-story and five-bay structure with chevron bracing system. According to the seismic design of structures if ductile elements is used in a structure, then beams and columns should remain elastic during earthquake, while ductile elements dissipate input energy by nonlinear behavior of ductile members. By considering of the results, the vertical link beam with length of 20 and 25 centimeter for far field earthquakes and 20 centimeter for near field earthquakes have the best performance compare to the other cases. The Bam earthquake is selected to investigate of hysteresis diagram of the vertical link beam energy dissipation. The results for near field earthquake like the Bam earthquake show that link beam with length of 40 centimeter with moment behavior, has low energy dissipation capability. Furthermore, the vertical link beam with 40 centimeter length causes more residual displacement and yielding. By considering the station with equal 104.28 km distance from center of earthquake can use the Bam record as a far field earthquake. In this case link beams with more than 25 centimeter length have more fluxing. However, the link beams with length of 20 and 25 centimeter have better seismic performance. Considering the RMS (Root Mean Square) parameter as a controller criterion the vertical link beam with length of 20 centimeter is more suitable for near and far field earthquakes. Considering the seismic performance parameters of vertical link beam like appropriate stiffness, high stability, energy dissipation capability, appropriate control of maximum response of structure and less residual displacement, the vertical link beam with length of 20 centimeter has the best seismic performance for near and far field earthquakes compare to the other cases.